I always wonder about this. Sometimes when I click the update tab, it doesn't show, then says no updates almost instantly. Then I click the update tab and it'll pop up and say it's available. Sometimes when clicking it, it'll say No update available almost instantly on click, other times it'll say searching for update for 10-20 seconds. Seems really strange. Never seen any other apps\OS work like this.
Get that behaviour too, but believe me, a restart won't do anything.